TouhouGD/render/shader/post_process2.gdshader

shader_type canvas_item;

uniform sampler2D screenTexture : hint_screen_texture;

void fragment() {
    vec2 screen_size = vec2(640,360);
    vec2 uv = UV;
    uv = floor(uv * screen_size / 0.2) * 0.2 / screen_size;

    COLOR = texture(screenTexture, uv);
}